1. Field of the Invention
The present invention relates to a sensor. More particularly, the present invention relates to a capacitive sensor.
2. Description of Related Art
Along with the progress of technology, a variety of sensors such as pressure sensors for sensing pressure, accelerometers, or acoustic sensors for sensing sound waves have been widely applied to electronic products. Taking the acoustic sensors for example, as the market has a demand for higher sound quality, the acoustic sensors are usually equipped with capacitive microphones of good signal quality.
FIG. 1 is a schematic view of a conventional acoustic sensor applied to a cell phone. Referring to FIG. 1, the acoustic sensor 100 uses a cover 110 to cover a micro-electro-mechanical system (MEMS) microphone 130 on a carrier 120. A rubber material 140 is filled in the cover 110, and an acoustic channel 150 in communication with the MEMS microphone 130 is reserved in the cover 110, such that sound waves are transmitted to the MEMS microphone 130 via the acoustic channel 150 so as to be converted into an electrical signal. It should be noted that since electronic products are developed to become lighter and thinner, the inner space is limited. The acoustic sensor 100 has an acoustic channel 150 therein, so the volume of the acoustic sensor 100 is too large to be disposed into an electronic product with a limited inner space.
Further, as shown in FIG. 2, U.S. Pat. No. 6,781,231 discloses a “MICRO-ELECTRO-MECHANICAL SYSTEM PACKAGE WITH ENVIRONMENTAL AND INTERFERENCE SHIELD.” The package structure 200 includes an MEMS microphone 210, a carrier 220, and a metal cover 230. The carrier 220 is used for carrying the MEMS microphone 210. In addition, the metal cover 230 has at least one acoustic port 240 that allows sound waves to reach the MEMS microphone 210.
However, the fabrication of the package structure 200 has difficulties and limitations. In detail, it is difficult to fabricate the acoustic port 240 in the metal cover 230 since the metal cover 230 is very thin. On the other hand, if the acoustic port 240 is formed in a side surface of the metal cover 230, the size of the acoustic port 240 will be limited by the height of the metal cover 230, such that the height of the package structure 200 cannot be further reduced, which is against the purpose of a light and thin product.
Besides, during packaging, a machine is employed to adsorb the metal cover 230, so as to attach the metal cover 230 on the carrier 220 for covering the MEMS microphone 210 in the conventional art. If the acoustic port 240 is disposed at the top of the metal cover 230, when the machine adsorbs the metal cover 230, the adsorption range of the machine may cover the acoustic port 240, such that the adsorptive power generated by the machine may easily damage the membrane of the MEMS microphone 210, thus resulting in a poor product yield.